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" has a " relationship

Hung Chang
Greenhorn

Joined: Oct 21, 2001
Posts: 16
can anyone explain to me what exactly is "has a" relationship..
thanx in advance
Michael Bruesch
Ranch Hand

Joined: Sep 23, 2001
Posts: 158
The "is a" relationship, as I assume you know, is inheritance, when one class extends another. Say you have a class "Plane" and another class "CommercialAirliner". A commercial airliner "is a" plane, therefore it would extend class Plane.
The "has a" relationship is what is called "aggregation". If you design a class called "Engine", and then design a class called "Car". A car "has a" engine. Therefore it would not extend engine, because a car is not an engine. It would therefore include an object of type Engine as one of its instance members.
Hope that's clear.
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Michael J Bruesch
Codito, ergo sum...
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